1. Field of the Invention
The present invention relates to planar antennas, used in electromagnetic communication systems. In particular, the present invention is directed to planar, printed antennas that utilize microelectromechanical systems (MEMS) based switching and actuating devices or circuits.
2. Description of Related Art
Miniaturization of mechanical systems promises unique opportunities for new directions in the progress of science and technology. Micromechanical devices and systems are inherently smaller, lighter, faster, and usually more precise than their macroscopic counterparts. However, development of micromechanical systems requires appropriate fabrication technologies which enable: the definition of small geometries; precise dimensional control; design flexibility; interfacing with control electronics; repeatability, reliability, and high yield; and low-cost per device.
When these micromechanical devices, such as fluid sensors, mirrors, actuators, pressure and temperature sensors, vibration sensors and valves, can form microelectromechanical systems (MEMS). Typical MEMS devices combine sensing, processing and/or actuating functions to alter the way that the physical world is perceived and controlled. They typically combine two or more electrical, mechanical, biological, magnetic, optical or chemical properties on a single microchip.
In recent years MEMS based switching and actuating devices have emerged as a viable alternative to solid state control devices in microwave systems. The MEMS devices offer many advantages. These advantages include significant reduction in insertion loss, which results in higher figure-of-merit and the MEMS devices consume insignificant amount of power during operation, which results in higher efficiency. Also, the MEMS devices have higher linearity, hence lower signal distortion, when compared to semiconductor devices. In addition, it has been also demonstrated that MEMS based switches and actuators can enhance the performance of antennas.
Last, MEMS actuators have the potential to dynamically reconfigure the frequency, polarization, and radiation pattern of antennas thus providing total reconfigurability. The capability to dynamically reconfigure the radiation patterns of planar antennas through geometric reconfiguration is essential for undertaking diverse missions. These advantages have been the motivation to integrate MEMS switches/actuators with planar antennas for beam steering and frequency/polarization reconfiguration.
For example, a patch antenna on a suspended micro-machined fused quartz substrate that can rotate can perform spatial scanning of the beam, as discussed in D. Chauvel, N. Haese, P.-A. Rolland, D. Collard, and H. Fujita, “A Micro-Machined Microwave Antenna Integrated with its Electrostatic Spatial Scanning,” Proc. IEEE Tenth Annual Inter. Workshop on Micro Electro Mechanical Systems (MEMS 97), pp. 84-89, Nagoya, Japan, Jan. 26-30, 1997. A Vee-antenna with moveable arms constructed from polysilicon material can steer as well as shape the beam, as discussed in J.-C. Chiao, V. Fu, I. M. Chio, M. DeLisio and L.-Y. Lin, “MEMS Reconfigurable Vee Antenna,” 1999 IEEE MU-S Inter. Microwave Symp. Dig., Vol. 4, pp. 1515-1518, Anaheim, Calif., Jun. 13-19, 1999. Furthermore, a field programmable metal array consisting of several thousand microswitches placed along the perimeter of a patch antenna can provide frequency reconfigurability, as discussed in S. M. Duffy, “MEMS Microswitch Arrays for Reconfigurable Antennas,” Notes of the Workshop “RF MEMS for Antenna Applications,” 2000 IEEE Ant. & Prop. Inter. Symp., Salt Lake City, Utah, Jul. 16, 2000.
Even taking these examples into account, the prior art has not demonstrated a polarization reconfigurable patch antenna made by use of integrated MEMS actuator. Thus, there is a need for a nearly square patch that can dynamically reconfigure the polarization from circular to linear, thus providing polarization diversity. There is also a need for a MEMS actuator that is housed within the patch and does not require additional space. This feature is particularly important in the construction of a N by N planar array antenna with small inter-element spacing.